package com.koomii.myproject.mybatis.dialect;

import com.koomii.myproject.mybatis.Dialect;


/**
 * <dl>
 * <dt>MySQLDialect</dt>
 * <dd>Description:Mysql方言</dd>
 * </dl>
 * @author david
 */
public class MySQLDialect implements Dialect {

	@Override
	public boolean supportsLimit() {
		return true;
	}

	@Override
	public String getLimitString(String sql, int offset, int limit) {
		return getLimitString(sql, offset, Integer.toString(offset),
				Integer.toString(limit));
	}
	
	/**
	 * 将sql变成分页sql语句,提供将offset及limit使用占位符号(placeholder)替换.
	 * <pre>
	 * 如mysql
	 * dialect.getLimitString("select * from user", 12, ":offset",0,":limit") 将返回
	 * select * from user limit :offset,:limit
	 * </pre>
	 *
	 * @param sql               实际SQL语句
	 * @param offset            分页开始纪录条数
	 * @param offsetPlaceholder 分页开始纪录条数－占位符号
	 * @param limitPlaceholder  分页纪录条数占位符号
	 * @return 包含占位符的分页sql
	 */
	public String getLimitString(String sql, int offset, String offsetPlaceholder, String limitPlaceholder) {
		StringBuilder stringBuilder = new StringBuilder(sql);
		stringBuilder.append(" limit ");
		if (offset > 0) {
			stringBuilder.append(offsetPlaceholder).append(",").append(limitPlaceholder);
		} else {
			stringBuilder.append(limitPlaceholder);
		}
		return stringBuilder.toString();
	}
	
	@Override
	public String getCountString(String sql) {
		return "select count(1) from (" + sql + ") as tmp_count";
	}
}
